Cargo containers (hereinafter “containers”) are used for shipping freight on commercial transport carriers such as cargo ships, railcars and trailers. “ISO” containers are a common type of container designed according to ISO (International Standards Organization) specifications which ensure that the containers are inter-operable with compatible carriers. One feature of ISO containers is a hollow lifting block in each corner of the container for securing the container to compatible equipment. The lifting block has a central cavity, and a generally rectangular opening permits access to the cavity from the exterior of the container. In order to secure the container to the compatible equipment, a bayonet or twist lock is inserted into each lifting block and a compatible fitting on the equipment. The twist lock has a spindle section on one end and a wide key section of generally rectangular profile on the end opposite the spindle section. The spindle section is captured by the fitting on the compatible equipment. The key section of the twist lock is inserted through the opening and into the central cavity of the lifting block. The twist lock is twisted or rotated ninety degrees about the spindle axis and relative to the cavity walls between an open position and an engaged position. The open position permits the rectangular key section to be inserted through and freely removed from the rectangular opening of the lifting block. When rotated to the engaged position, the rectangular key section engages the lifting block and permits vertical force to be applied to the lifting block for hoisting the container.
In some terminal facilities, dedicated and specially designed high-speed handling equipment is used to rapidly hoist and move high volumes of ISO containers between carriers or between a dock and carrier. High speed handling equipment designed for hoisting containers can include automated or remotely controlled twist locks for engaging the container, or automated grapple arms for grabbing the container. Such high speed handling equipment is dedicated solely for handling containers and is not useful in a terminal facility where other loads must also be moved. High speed handling equipment for containers also requires a large footprint for operation. High speed handling equipment for containers also requires a large capital investment.
In view of the foregoing, many terminal facilities have only a general purpose crane or hoist equipment (hereinafter “hoist equipment”) for handling ISO containers, non-ISO containers and other loads. Off-shore oil platforms are examples of terminal facilities where containers are handled with general purpose hoist equipment. As used herein, “hoist equipment” includes any overhead hoist equipment or crane providing a single point lift or having a hoist cable and terminal fitting, such as a hook, which is raised and lowered to move a load such as a container. A container or load to be hoisted is manually attached to the hook, such as by using wire rope slings. In some terminal facilities, empty containers are attached directly to the wire rope slings and raised. However, using this type of direct attachment to hoist a container is dangerous and can subject the container to stresses which damage the container or cause immediate failure of the container. These dangers and the risk of damaging the container are greatly increased when the container is loaded. Hoisting a container carrying a cargo load that has uneven distribution of weight throughout the container is more dangerous and further increases the risk of damaging the container.
Moving containers from a supply boat to an off-shore oil platform with general purpose hoist equipment can be particularly dangerous and presents a greater risk of damaging the container. The danger and risk are compounded by motion of the supply boat relative to the oil platform and hoist due to waves, wind and surface currents. Due to motion of the supply boat, the container on the deck of the supply boat when attached to the hoist can be jerked and subjected to additional stress in the form of sudden horizontal and vertical forces. When clear of the deck of the supply boat, the container can swing and hit projecting structure within the tight confines of the oil platform before coming to rest on the oil platform. Similar forces can be encountered when moving containers from the oil platform to the supply boat.
General purpose hoist equipment can be used to safely hoist a loaded container with a spreader frame attached to the hook and to the container. The spreader frame is adapted to permit the container to be hoisted without exposing the container to excessive bending stress and without applying horizontal forces to the container and twist locks. The spreader frame has a rigid frame structure which is attached to the hoist hook by a set of wire rope slings. The spreader frame includes four twist locks on the rigid frame structure at locations corresponding to the lifting blocks of the container. The twist locks are received in the lifting blocks and thus attach the container to the spreader frame. When the spreader frame is hoisted by operation of the hoist equipment to raise the hook, both vertical and horizontal force components are transmitted through the wire rope slings to the rigid frame structure. The rigid frame structure absorbs horizontal force components, such that only vertical forces are transmitted to the container by the twist locks attaching the container to the rigid frame structure of the spreader frame. The rigid frame structure supporting the twist locks and container attached thereto also reduces bending stress on the container.
A problem associated with hoisting ISO containers with a spreader frame is that one or more of the twist locks can be unintentionally or accidentally rotated to the open position before the spreader frame and attached container are hoisted, or while the spreader frame and attached container are suspended from the hoist. Hoisting a spreader frame with the container secured thereto by only three or fewer twist locks can be dangerous and risks damaging the container, cargo, equipment and personnel.
Gross weight capacity is one limiting mechanical factor of containers. Increasing gross weight causes increased bending stress on the container walls when the loaded container is hoisted from a resting position.
Overall length is a limiting mechanical factor for containers. Increasing overall length causes increased bending stress on the container walls when the container is hoisted from a resting position, particularly when the container is loaded.
Bending stress is a limiting mechanical factor for containers. Bending stress causes deflection of the container walls when the loaded container is hoisted from a resting position, particularly of the longitudinal walls extending between the ends of the container. Excessive bending stress can cause the container walls to fail by buckling.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an improved spreader frame for hoisting cargo containers.